1. Technical Field
This invention relates generally to the field of ophthalmology, and more particularly to an aid for inhibiting passage of topically applied eye medication into the patient's bloodstream.
2. Background Art
Topical medications, in the form of drops or ointment, are frequently used in treatment of many eye disorders, such as glaucoma. Though such medications are beneficial when restricted to the immediate region of the eye itself, some of them, if absorbed into the patient's bloodstream, can cause profound negative side effects in many different parts of the body, such as the heart, pulmonary system, liver, pancreas, brain, and can even result in sexual disfunction.
Topical eye medications can make their way into the patient's bloodstream by way of the lacrimal system of each eye. The lacrimal system includes glands and structure for both producing beneficial tears, and for drainage of tears from the eye.
The space between the exterior of a normal eye and the interior of surrounding tissues can accommodate only about ten microliters of fluid, be it tears or artificially introduced fluid such as topical eye medication. A normal drop from a medicine dropper or bottle ranges from about 25 to 50 microliters. It can therefore be seen that, when topical eye medication is administered, the volume of the medication far exceeds the capacity of the eye to accommodate the extra fluid. It is therefore evident that a relatively large fraction of the administered medication will drain from the eye through the lacrimal system and into the patient's nasal cavity.
Tears, a complex solution, are produced by lacrimal glands located under the eyelids. Excess tears are both dissipated by evaporation and by drainage through the lacrimal system. The lacrimal system includes upper and lower puncta, located on the interior of the upper and lower eyelids, respectively. The puncta are orafi which communicate respectively with canalicular canals, which in turn lead to a lacrimal tear sac. The tear sac communicates with a channel known as the nasolacrimal duct, which leads into the patient's nasal cavity. The nasal cavity is lined with thin mucus membrane which has a high facility for absorbing incident chemicals into the patient's bloodstream.
Therefore, when topical eye medication is administered, some of it is carried away by the natural flow of tears and ends up in the patient's nasal cavity, from which a certain amount of that medication is subsequently absorbed into the patient's bloodstream through the nasal mucosa. Carried by the bloodstream, the medication makes its way to virtually all parts of the patient's body. If the medication is of a type which can cause negative side effects, such transport is undesirable.
Movement of fluid through the lacrimal system is assisted by blinking of the eyes. This phenomenon is sometimes referred to as "the lacrimal pump". Conversely, if the eyes are kept gently closed, fluid movement through the lacrimal system is usually reduced.
It is known that, when topical eye medication is administered, much of the dose is actually absorbed into the eye within a few minutes after administration. Therefore, it is possible to reduce the amount of medication which is transmitted by the lacrimal system into the patient's nasal cavity and subsequently into his bloodstream by inhibiting only temporarily the flow of tears through the lacrimal system into the patient's nasal cavity. Usually, inhibiting lacrimal flow for about five minutes after administering topical eye medication is sufficient to satisfactorily reduce the amount of medication which ultimately ends up in the patient's bloodstream.
It is known that a patient can inhibit his lacrimal flow by the use of gentle digital pressure, usually applied in the general area of the eyelids nearest the nose. For patients with arthritis, long fingernails or disorders making hands unsteady, this technique has disadvantages, and sometimes cannot be practiced at all.
Physicians sometimes recommend that a patient keep his eyes gently closed after administering topical eye medication. This advice is intended to reduce the amount of lacrimal flow, and therefore to correspondingly reduce the amount of eye medication delivered to the patient's nasal cavity by the pumping action which blinking would otherwise cause.
Surgically implanted devices are known for either partially or totally obstructing lacrimal flow. These devices, however, are designed as permanently in-dwelling implements, and are not designed to be readily removed except by an appropriately trained physician. They do not, therefore, lend themselves to temporary, short-term reduction of lacrimal flow. Rather, such implements are designed for patients who have a condition often called "dry eye", in order to reduce drainage of lacrimal fluid from the eye and, therefore, facilitate retention of tears keeping the eye moist.
A general object of the present invention is to provide apparatus and method for facilitating topical eye treatment by controlling fluid flow through the lacrimal system without the need for application of digital pressure.